This work was supported by grants (to S.W.L.) from the National Science Council (grant nos.: NSC93-2314-B002-276, NSC94-2320-B002-092, 95-2320-B-002-054, NSC95-3112-B-002-017, 96-3112-B-002-023, and NSC98-3112-B-002-030), the National Health Research Institutes (grant nos.: NHRI-EX90-9142SI, NHRI-EX91-9142SI, NHRI-EX92-9192SI, and NHRI-EX99-9729BI), National Taiwan University Hospital, Taiwan (grant nos.: 90A01 and 91A06), and a grant (to H.P.H.) from the National Science Council (NSC 97-2321-B-002-020-MY3).